1. Field of the Invention
The present invention relates to a subject information acquisition apparatus and a subject information acquisition method for acquiring subject information of a subject by receiving an elastic wave. In this description, the elastic wave is a concept including a sound wave, an ultrasonic wave, an acoustic wave, a photoacoustic wave, and an optical ultrasonic wave.
2. Description of the Related Art
Photoacoustic imaging (PAI) attracts attention as a method for specifically imaging angiogenesis caused by cancer. The photoacoustic imaging is a method for irradiating illumination light (near-infrared light or the like) to a living organism or the like and receiving photoacoustic waves generated from the inside of the living organism by a probe to make an image. As a method for acquiring an image inside a living organism by using a principle of the photoacoustic imaging, photoacoustic mammography (PAM), whose subject is a breast, is disclosed in Srirang Manohar, et al., The Twente photoacoustic mammoscope: system overview and performance, Physics in Medicine and Biology 50 (2005) 2543-2557.
FIG. 4A is a schematic side view of a measuring method of the above document. In FIG. 4A, an Nd:YAG laser 107a is a light source that illuminates the subject (breast). An illumination optical system 107 guides laser light emitted from the Nd:YAG laser 107a to the subject and illuminates the subject. An illumination system scanning mechanism 108 includes the illumination optical system 107 and causes the illumination optical system 107 to scan in a vertical direction (a direction indicated by an arrow in FIG. 4A) and a horizontal direction (a direction perpendicular to the page of FIG. 4A). The probe 102 receives a photoacoustic wave generated from the subject. A signal processing unit not shown in FIG. 4A selects a receiving device of the probe 102 that acquires a signal to form an image from an illumination position set by the illumination system scanning mechanism 108, amplifies the signal, converting the signal into a digital signal, and reconstruct the image. A holding plate 105 made of glass transmits illumination light from the illumination optical system 107 and compresses and holds the subject between the holding plate 105 and the probe 102. A subject person lies on her stomach on a bed not shown in FIG. 4A and inserts her breast, which is the subject, into an insertion hole in the bed. The subject is compressed and held between the probe 102 and the holding plate 105. The apparatus disclosed in the above document acquires image data in a living organism from a photoacoustic signal by a measuring method shown in FIG. 4A.
A multifunction device including an X-ray mammography machine and an ultrasonic device as shown in FIG. 4B is disclosed in U.S. Pat. No. 6,607,489. The device shown in FIG. 4B compresses and holds a subject not shown in FIG. 4B between a first holding plate 101 and a second holding plate 105 by moving the first holding plate 101. A small probe 102 which can move along a surface of the first holding plate 101 is provided on the first holding plate 101 on the opposite side of the subject. The probe 102 is held by a gantry 103 which functions as a guide. The probe 102 transmits an ultrasonic wave to the subject through the first holding plate 101. The device shown in FIG. 4B acquires an ultrasonic image in the subject by using a signal generated from a wave reflected from the subject and received by the probe 102.
However, as disclosed in U.S. Pat. No. 6,607,489 and Srirang Manohar, et al., The Twente photoacoustic mammoscope: system overview and performance, Physics in Medicine and Biology 50 (2005) 2543-2557, in elastic wave imaging in which an elastic wave is received and the subject information is acquired from a received signal while the subject is held by the plates, it is desired that the image quality is further improved.